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```Appendix III.

947

The theoretical thermal efficiency of any gas engine may be
found from the formula

/r - 4

where the suffixes stand for release, exhaust, ignition, and atmo-
sphere respectively.

The  expansion curve  is ^V1*38 = C,  and  the  compression
curve is/V1^ = C.

Oil-Engine Trials.—The balance sheet is of exactly the
same character as that of the gas engine. Taking the items
separately.

(i) Heat of combustion due to oil per min. is found as before,
being about 19,000 B.T.U. per Ib. wt; and the heat already in
the air and oil must be obtained as follows:

,    B.T.U. per m.
w         in oil

•169 (/- 32) x Ibs. per m.
specific ht. x (t ~~ 32) x Ibs. per m.

The specific heat of petroleum averages '45.

(2), (4), and (5).   These quantities need no further explanation.

(3) Heat discharged in exhaust pipe. — The exhaust gases
consist of CO2 and air. In addition, however, on account of the
large proportion of hydrogen in the oil, there is a considerable
quantity of water formed, amounting to nearly half the weight of
the gaseous products. The method of procedure is somewhat
similar to what obtains on p. 938. Thus:

(a)  Analyse the oil to find % C and H.

(b)  Find the % volumetric composition of the exhaust gases,

and transform at once into % weight composition
(see a, p. 938).

(c)  Find weight of CO2 per lb< of oil, from

lb.C+a-661bs.O) - ^(3-661bs.COa)...gn6e```